The prognosis for men with prostate cancer extending beyond the anatomic boundaries of the prostate gland is poor due to early dissemination of disease that cannot be eradicated by currently available systemic therapies. Understanding the mechanisms leading to therapy resistance is a prerequisite to the development of effective treatments. These mechanisms remain poorly understood and progress has been stymied by the limitations of currently available pre-clinical models coupled with the inability to evaluate mechanisms of resistance in vivo due to lack of pre- post-therapy tumor specimens. Molecular studies of prostate cancer involving the analysis of gene expression profiles have demonstrated remarkable heterogeneity in the genetic make-up of primary and advanced prostate cancers that could lead to substantial inter-individual variation in response or resistance to therapy, based on intrinsic characteristics of the tumor. This proposal is based on the hypothesis that tumor response and resistance mechanisms can be identified through the comparative analyses of in vivo gene expression profiles acquired before and after the administration of cytotoxic drugs. Once identified, these tumor resistance mechanisms can be exploited through the design of combination therapies targeted toward circumventing these pathways. We further hypothesize that pretreatment gene expression profiles will be indicative of response to specific therapies, such that individualized treatments can be selected for optimal efficacy. This proposal will overcome previous obstacles by using tissue and clinical data from a unique prospective clinical trial of neoadjuvant cytotoxic chemotherapy in patients with high-risk prostate adenocarcinoma to identify molecular alterations correlating with clinical and pathological indicators of tumor response. The functional relevance of the molecular targets will then be examined in in vitro systems and effects of targeting these specific drug-resistance mechanisms on tumor response to chemotherapy will be examined using in vitro and in vivo. We seek to identify novel treatment targets by comparing cancer cells that survived chemotherapy to those collected prior to treatment in patients treated in a unique study of pre-operative chemotherapy for prostate cancer. We will test the effectiveness of novel treatments that exploit newly discovered targets in the laboratory and lay the foundation for human trials to develop effective prostate cancer treatment.